1. Field of the Invention
This invention relates to a resistor for audio equipment adapted for use in a high-fidelity amplifier in audio equipment.
2. Prior Art Description
In audio equipment, a high-fidelity amplifier is used to amplify the low level signals and reproduce sounds with good quality. Even slight variations in the electrical characteristics of the resistors used in high-fidelity amplifiers result in a major degradation of the sound quality. This has given rise to proposals to suppress variations in the characteristics of resistors caused by extraneous signal noise, to prevent the amplifier circuitry from being adversely affected.
JP-A 61-34901, for example, discloses an induction array of resistors for audio equipment applications in which, in order to improve the quality of reproduced sound, the induction field generated when electricity passes through the resistance film is utilized to minimize distortion with respect to the signal current.
In another example, JP-A 3-288401 relates to a shielded resistor comprising alternating layers of a magnetic film and a conductive film, in which extraneous noise is converted into heat energy, which is radiated away to prevent noise affecting the resistor in the shielding.
In another disclosure, JU-A 1-130501, the inside surface of the resistor carrier is formed in strips and the outside of the carrier is covered with shielding.
In all of the prior art resistors, the surface of the resistance film is sheathed to insulate the resistance film from the outside air. In one method, for example, the sheathing is coated on. The sheathing is usually a dielectric, so it is readily charged by external electrostatic induction. When this happens, there is a high possibility of the charge carriers causing variation in the electrical characteristics of the resistance film.
Moreover, when a magnetic sheathing is used, there is a high risk of the magnetism giving rise to phase distortion of signals applied to the resistor.
When the resistor carrier is cylindrical and comprises strips of resistance film on the inside surface and shielding on the outside surface, the shielding prevents the resistance film from being affected by the magnetism. However, with the shielding and resistance film being formed integrally with the resistor carrier, the signal flowing through the resistance film charges the resistor carrier, which can adversely affect signals applied to the resistor.
Also, a CLT-1 tester (made by Radiometer AS Copenhagen) or the like can be used to test the linearity of such resistors. At more than 120 db, the third high-frequency component included in a 10 KHz signal is known to be low. However, an examination into the factors causing variations in the characteristics of such resistors revealed the following. The present inventor used a Hewlett-Packard 4284A LCR Meter to measure the inductance produced when resistance films are subject to spiral cutting, and the capacitance resulting from using sheathing to directly protect the resistance films. At high audio frequencies, no inductance component was detected, just a change in the capacitance component of 40 db or more.
These results reveal that the sound sensitivity is affected not by the inductance component of the resistor, but only by the capacitance component, which depends on the dielectric sheathing. That is, the sheathing is in direct contact with the resistance film and therefore is charged by electrostatic induction, thereby affecting signals applied to the resistance film.
Based on these findings, the object of the present invention is to provide a resistor for audio equipment that is able to prevent audio replay containing unusual sound quality caused by the effect on the characteristics of a resistance film caused by the resistor sheath becoming charged by electrostatic induction.